In the dental technology, a plurality of synthetic materials, so-called composites, are known which polymerize due to a metacrylate based curing mechanism when irradiated with light. As the essential photo-initiator these materials contain camphor quinone or phosphine oxide which absorbs a broad band within the blue spectral range, with an absorption maximum at about 472 nm and 430 nm, respectively.
Depending on the color of the material, the polymerization reaction requires light having an intensity of at least 1 to 5 mW/cm.sup.2 within a very thin layer. In the practice of polymerizing tooth stoppings or dental replacement parts, a light intensity of at least 250 mW/cm.sup.2 is required within an appropriate period of time to achieve polymerization of sufficient degree and depth. Commercially available dental polymerization apparatus emit light at an intensity of about 400 to 500 mW/cm.sup.2, sometimes up to 700 mW/cm.sup.2.
Desk apparatus are known in which the light is generated and focused within the apparatus and transmitted to the treatment site within the patient's mouth by means of a flexible optical waveguide having a length of typically 1.5 to 2 m. In addition to a substantial loss of light that occurs at its input and output faces, such an optical waveguide usually has a diameter of about 10 to 15 mm and is therefore relatively stiff and unwieldy.
In other prior-art apparatus, such as known from, e.g., German Offenlegungsschrift No. 3,840,984, the light is generated and focused within a gun-shaped hand piece and transmitted to the treatment site by means of a rigid light conducting rod made of fibers or quartz. A chief disadvantage of these apparatus results from a considerable heating of the hand piece and, as that is held close to the treatment site, of the irradiated location itself. Moreover, the power supply cable required in this type of apparatus for feeding current to the hand piece is considered troublesome.
German Offenlegungsschrift No. 4,211,230 discloses a battery-powered apparatus which is independent of the mains or a power supply unit but requires comparatively large and heavy batteries to provide the necessary high electric output, and is thus difficult to handle.
The known photopolymerization apparatus often employ tungsten-halogen lamps which emit light in a comparatively wide spectral range, thus output the largest portion of their energy as heat and light in the red and green wavelength ranges. Only about 2 percent of the power input is emitted in a spectral range of about 400 to 515 nm, which is the range useful for the above-mentioned composite materials using camphor quinone or phosphine oxide as a photo-initiator.
Conventionally employed light sources have the further difficulty that their light output decays throughout their life in a manner that is not readily detected by the user, so that the quality of the polymerization deteriorates with time.
Another disadvantage resides in the fact that optical components such as lenses and reflectors are required in order suitably to image the helix of the lamp to the entry end of the waveguide and illuminate the full area of the entry end without losing light energy. Also, filters are needed to absorb the heat radiation and to reduce the halogen light of the desired spectral range. These optical components may also reduce the light output due to ageing and defects, thereby rendering a safe polymerization impossible.
It is a further disadvantage of known apparatus, specifically hand-held apparatus, that air circulation required for the removal of heat also causes a spreading of bacteria. Due to their open design, as is necessary for ventilation, and due to their size, these apparatus are difficult to sterilize and disinfect.